Archived posting to the Leica Users Group, 2001/12/05
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Jo Goodtimes wrote: > Hello Jerry . > I think I have an explanation but I'm not sure . > Since the diaphragm setting isn't coupled to the flash , > it only controls the areas exposed by natural light . > If you were in TTL mode , the cell behind the lens of your > M6 actually controlled the flash power . > Now this drives to a question : is it necessary to adjust the > diaphragm on the flash in TTL mode ? > Maybe not . As far as I understand, in TTL mode you don't need to tranfer the lens aperture setting to the flash, in spite of saying on page 40 of the manual that you must. You only need to tell the flash the lens aperture if you want to use the inbuilt max/min distance calculator, see page 50 in the manual. With the R8 the aperture is automatically communicated to the flash as soon as you apply first pressure to the shutter release and the distance display changes as you rotate the lens aperture ring. I think the way fill in works in TTL and A modes, is that the flash intensity is higher and shorter duration than the film illumination from the natural light falling on the scene. The flash may be 1/10,000 sec and the total film exposure 1/50 sec. This means the natural illumination has little effect on the flash metering circuits. The flash fill/exposure is determined by the lens aperture actually set on the lens, film speed (set by camera in TTL mode or manually on flash in A mode), +/- exposure compensation set on flash and scene reflectivity. For fill in I need to find the limits of film speed and maximum lens aperture when using an 85B filter (tungsten fill) over the flash with and without the diffuser. I suspect using 800 ASA Portra and f 1.4 - -2.0 I'll need a neutral density filter over the flash when in non TTL A mode. Bob Parsons bobp@dodo.demon.co.uk - -- To unsubscribe, see http://mejac.palo-alto.ca.us/leica-users/unsub.html